Though the RS-50 has a bit better contrast, you would have to open the IRIS up much sooner on the RS-50 because it is DIMMER than the RS-46.

I'd go with the RS-46 over the RS-50, otherwise check out the RS-55 if that's an option (sounds like its not), or maybe the RS4810. I think most would consider any of these a big upgrade over the RS-2, although a rare few might say otherwise, but yes it is a pretty big upgrade.